Exercise 2 relative and absolute dating of geologic events answers examples of speed dating questions

(G) High resolution GISP2 potassium (non-sea salt). Black curve, global temperature reconstruction by Marcott et al., 2013, from 73 proxies averaged by differencing and with the original published dates. Red curve, Bond et al., 2001 ice-rafted debris stack (inverted) from four North Atlantic sediment cores.

Notice that all Holocene abrupt climate changes are cooling events. Grey bars, cooling oscillations part of the ~2400 year Bray cycle.

Oscillations during an interglacial are smaller and are cooler (Bond) events, and oscillations become larger the colder temperatures become. Glaciation and Solar Activity since the Fifth Century BC and the Solar Cycle. This solar cycle, slightly shorter than he calculated, is now known as the Hallstatt cycle while, in justice, it should be named the Bray cycle.

During the glacial period oscillations are very large and are of a warming nature (Dansgaard-Oeschger events). The asterisk marks the current position, where we are very worried that the present warming is the ‘largest in thousands of years’ instead of being worried that the next cooling will also be bigger than the previous and will probably lead to glacial inception. Roger Bray recognized several major past cooling episodes and attributed them to a solar cycle. Since Bray’s report, other researchers have confirmed the reoccurrence of cooler climates with a periodicity of about 2400 – 2600 years by different techniques, glacial moraines, temperature-sensitive tree rings widths, and δO isotope and chemical analysis of sea salts and dust in ice cores (O’Brien et al., 1995).

These episodes give us an average spacing of ~ 2400 years and, at the same time, they define the major climatic states of the Holocene. Northern Hemisphere paleoclimate records showing main Holocene abrupt climate change events. (B) Western Mediterranean (Iberian Margin) core MD95-2043, sea surface temperature (SST) C37 alkenones. (D) North Atlantic Bond series of drift-ice stacked petrologic tracers. Vegetation changes suggest that they constitute distinctive climatic states established by insolation conditions from the obliquity and precession cycles (figure 47).The Neoglacial period is characterized by generalized glacier advances that take place coinciding with the decrease in Northern Hemisphere solar forcing. Cooling events during the HCO, like the 8.2 kyr event, were followed by a complete recovery of temperatures and globally glaciers reached their minimum Holocene extent in most areas between 6000-5500 years BP.However there is evidence that the world did not completely recover from the cooling events that took place between 56 BP, initiating the Neoglaciation.It has become a lot more difficult to identify these changes because their signal is much lower and more difficult to separate from the noise of small high frequency climatic variability.This has created much confusion about the nature and causes of Holocene abrupt climatic changes and has given many the false impression that the Holocene is characterized by long periods of climate stability. The Holocene is a period of almost constant climate change with climatic stability being the exception. Nature of climatic oscillations during the Ice Age.

Leave a Reply